Insights on E1-like enzyme ATG7: functional regulation and relationships with aging-related diseases

Autophagy is a dynamic self-renovation biological process that maintains cell homeostasis and is responsible for the quality control of proteins, organelles, and energy metabolism. The E1-like ubiquitin-activating enzyme autophagy-related gene 7 (ATG7) is a critical factor that initiates classic autophagy reactions by promoting the formation and extension of autophagosome membranes. Recent studies have identified the key functions of ATG7 in regulating the cell cycle, apoptosis, and metabolism associated with the occurrence and development of multiple diseases. This review summarizes how ATG7 is precisely programmed by genetic, transcriptional, and epigenetic modifications in cells and the relationship between ATG7 and aging-related diseases.

structure always appears in guanine-rich DNA sequences, regulating gene replication and transcription in cancer cells and neurons 13 .G4ligand pyridostatin can form 1:1 and 2:1 complexes with G4 in Atg7, inhibiting autophagy by stabilizing the G4-DNA complex 14 .Another distinct G4-DNA-binding ligand, BRACO19, can downregulate Atg7 transcription.The formation and disassociation of Atg7 G4-DNA is the original pathway for regulating autophagy in neurons, which correlates with the effect of age on memory 15 .
Nineteen DNA sequence variants (DSVs) containing single-nucleotide polymorphisms (SNPs) have been observed in the Atg7 gene promoter of coronary artery disease patients, including those with acute myocardial infarction (AMI).Multiple DSVs and SNPs alter the transcriptional activity of the Atg7 promoter by affecting the combination of transcription factors and Atg7 expression 16 .Genome-wide association studies and DNA methylation and exome sequencing data have identified 41 variants, 56 SNPs, and 38 SNPs of Atg7 associated with HDL-cholesterol, systolic blood pressure, and blood pressure, respectively 17 .Moreover, Atg7 variant rs8154 is a new prognostic marker for breast cancer based on in silico analysis 18 .
Parkinson's disease (PD) is a fast-growing neurological disorder and neurodegenerative disease 19 .Reduced Atg7 transcriptional activity was observed with four novel heterozygous variants and confirmed in five PD patients.Variations in the Atg7 gene promoter alter ATG7 protein levels in PD patients and influence autophagic activity, possibly contributing to the onset of the disease 20 .Furthermore, elevated plasma ATG7 levels in the Han population of South China may result in susceptibility to late-onset sporadic PD 21 .An SNP in the Atg7 gene can also impact the age of Huntington's disease (HD) onset 22 .A European HD Network study demonstrated the impact of Atg7 V471A polymorphism on the age of HD onset on Italians 23 .
Transcription factors and transcriptional regulators.The prominent transcription factor forkhead box O1 (FOXO1) is the main target of insulin signaling and is involved in interleukin-9 (IL-9) signaling pathways.FOXO1 is also a transcription-independent mediator of autophagy 24,25 .FOXO1 is acetylated by its dissociation from SIRT2, which determines its interaction with ATG7 and promotes autophagy under serum starvation 24,26 .The Ac-FOXO1-ATG7 complex activates autophagy independent of Beclin1 or Mechanistic target of rapamycin (mTOR) 24 .Under low oxidative stress (OS) conditions, FOXO1 maintains cell viability via its export from the nucleus, acetylation into Ac-FOXO1, and formation of the Ac-FOXO1-ATG7 complex.Under high OS levels, FOXO1 is located in the nucleus, promoting the transcription of proapoptotic proteins and apoptosis 27 .Most FOXO1 DNA-binding domain mutants preserve their interaction with cytoplasmic ATG7 28 .Moreover, the interaction between ATG7 and phosphorylated FOXO1 in the cytoplasm of immature natural killer (NK) cells is essential for NK cell maturation 29,30 .The FOXO1-ATG7 complex is also associated with bone formation and bone-related disorders 31 .
FOXO3, another Atg7 transcriptional regulator, is predicted to bind Atg7 at the ENCODE H3K4Me1 site 850 bp upstream of the Atg7 transcription start site.FOXO3a-transactivated ATG7 acts as a tumor suppressor in non-small cell lung cancer (NSCLC) and mediates CK1α-induced autophagy, an anti-neoplastic mechanism 32 .Additionally, cellular redox imbalance and mitochondrial dysfunction in Atg7-KO mouse embryonic fibroblasts (MEF) cells are partly abrogated by FOXO1/3 overexpression through the restoration of antioxidant enzymes and reactive oxygen species (ROS) suppression 33 .
Heat shock factor 1 (HSF1) is a transcription factor and main regulator of temperature stress responses implicated in tumorigenesis 34 .HSF1 can directly bind to the promoter of Atg7 to increase its expression, which is necessary for the cytoprotective autophagy induced by chemotherapeutic agents 35 .Furthermore, miR-217 induces HSF1/ATG7 pathway signaling by limiting NF1 expression and enhancing breast cancer cell autophagy, leading to chemoresistance 36 .During starvation, PSMD10 transfers to the nucleus and cooperatively binds to the Atg7 gene promoter with nuclear HSF1 to upregulate ATG7 expression 37 .NBAT1 suppresses Atg7 transcription by promoting PSMD10 degradation and inhibits PSMD10 and HSF1 occupancy on the Atg7 promoter, inhibiting autophagy and chemoresistance in NSCLC 38 .
Transforming growth factor-β1 (TGF-β1) is a cytokine that increases the expression of autophagy-related genes, including Atg7 39 .TGF-β1 function is partly mediated by its regulation of Y-box binding protein 1 (YB-1), which binds to the Atg7 promoter.The nuclear translocation of YB-1 induced by TGF-β1 promotes Atg7 transcription and participates in the liver injury 40 .TGF-β1 is also a common fibrosis marker involved in multiple diseases.TGF-β1 and ATG7 play roles in fibrosis in many tissues in an autophagy-dependent manner.During maladaptive kidney repair, autophagy stimulates fibrogenesis by fibroblasts via the pro-fibrotic factor, fibroblast growth factor 2 41 .In contrast, ATG7-mediated autophagy  suppresses vocal fold injury-induced fibrosis 42 .The TGF-β1/ATG7 axis is also involved in fibrosis in unilateral ureteral obstruction, SiO 2 -induced pulmonary inflammation, and radiation-induced skin injury, making autophagy a potential therapeutic target in fibrosis [43][44][45] .
Signal transducer and activator of transcription (STAT) 3 is activated by phosphorylation and forms homo-or heterodimers.It binds to the Atg7 promoter, upregulating ATG7 expression.The IL-6/Janus kinase (JAK)/ STAT3 pathway modulates skeletal muscle atrophy by regulating ATG7mediated autophagy 46 .The inhibition of STAT3-mediated autophagy by ATG7 might be a novel target in triple-negative breast cancer 47 and denervation-induced muscle atrophy 48 .Autophagy can increase the expression of pro-inflammatory cytokines, including IL-6 and IL-8 49,50 .These reports indicated that ATG7 might connect autophagy and inflammation.
Retinoid acid receptor is a transcription factor that can bind to the 5'flanking region of the Atg7 proximal promoter, regulating ATG7 transcription and hepatocellular carcinoma (HCC) progression .CAMP response element-binding protein (CREB) is a transcriptional regulator that binds to the Atg7 promoter at the −1809 to −1412 region.P38/Hsp27/ CREB/ATG7 pathway signaling affects HCC chemoresistance by regulating autophagy 52 .Transcription factor NRF1 stimulates the Atg7 promoter 53 , promoting autophagy in human nucleus pulposus cells 54 .Besides raising Atg7 mRNA levels, EVI1 can also increase intracellular ROS levels involved in EVI1-induced autophagy.Therefore, EVI1 might promote drug resistance via dual control of ATG7 55 .
DNA methylation of Atg7 gene.DNA methylation modulates multiple biological functions, including signal transmission, DNA repair, and gene Renal proximal tubule-specific Atg7-KO mice are significantly more sensitive to cisplatin-induced AKI.

Liver
Loss of autophagic function inhibits lipid release and hepatic fibrogenesis in ATG7-interferred hepatic stellate cells.

Intestine
The intestinal epithelial-specific ATG7 deficiency in mouse model has a negative influence on the regenerative benefit of calorie restriction, partly caused by the function of ATG7 in modulating luminal glycocholic acid, which is crucial to the self-renewal of epithelial stem cell.
Unlike the oncogene role of ATG7 in colon cancer, the researches about inflammation-associated colon tumorigenesis in intestinal epithelial-specific Atg7-KO mice show a negative effect on tumorigenesis of colitis-associated cancer.
Intestinal ATG7 deficiency causes intestinal dysbiosis, which leads to a suppression of tumor initiation and growth.
Pancreas Impaired glucose tolerance is observed in pancreatic β cell-specific Atg7-KO mice, along with the accumulation of p62, which is required for cellular homeostasis regulation.
Researches in ATG7-deleted β-cells with both long-term and short-term HFD mouse model employed, exhibit that shortterm ATG7 deletion benefits β-cell function and enhance glucose-stimulated insulin secretion, while the long-term is opposite.

Lung
Silencing ATG7 in lung-to-lung metastasis mice can turn the reduction of tumor nodules and cancer cell metastasis caused by increasing TIMP1.

Tissue Adipose
In adipocyte-specific Atg7-KO mice, HFD-induced inguinal white adipose tissue hypertrophy is promoted.

Skin
In ATG7-negative keratinocytes, autophagy induced by UVA or UVA-oxidized phospholipids is interrupted, which further causes obstructed removal of protein aggregates and oxidized phospholipids.
Researches carried out in ATG7-inactivated epidermal keratinocytes exhibits that corneocytes on the back of mutant mice is intensified.
ATG7 deletion in EC assists skin wound healing via promoting paracrine regulation.

Neuron
Excitatory forebrain neurons-specific ATG7 deletion in mouse model markedly inhibits Aβ secretion, which is the pathological character of AD.
Mitochondrial hyperfusion is found in ATG7-deficient astrocytes, which plays a key role in cell fate specification during autophagy

Muscle
In L6 skeletal muscle cells, iron-induced ROS production accompanied by apoptosis is enhanced by ATG7 deficiency.
VSMC-specific Atg7-KO mice suffer an elevation in aortic stiffness, and then compensatory mechanisms might be switched to maintain circulatory homeostasis.
During the diabetic courses, AGEs are able to active vascular smooth calcification and apoptosis, which can be inhibited by ATG7 deficiency.
Skeleton and Blood Compared with WT mice, the osteoblasts-specific Atg7-KO ones have markedly lower relative bone formation rate.Furthermore, the interruption of autophagy causes a decrease in bone volume, thickness, stiffness, and ultimate breaking force.
ATG7-deficient neutrophil precursors are observed to enhance glycolytic activity enhancement and lipid droplet accumulation, but impair mitochondrial respiration and reduce ATP production.
ATG7 deletion in murine BM-MNCs has a negative effect on STAT3 activation accompanied by its nuclear translocation.ATG7-mediated autophagy can protect BM-MNCs from radiation-induced genotoxic stress.
expression 56 .Legionella Infection can irreversibly change the GATC motif to G(6 mA)TC in the Atg7 promoter region, causing a time-dependent reduction in Atg7 mRNA, which further inhibits autophagosome formation.These findings about host defense against Legionella, including autophagy, might help prevent and treat Legionnaires' disease 57 .
Atg7 was one of five hub DNA methylation-regulated genes in the Framingham heart study.Studies in monocytes and peripheral blood leukocytes showed that the Atg7 methylation and expression status might be a novel epigenetic mechanism for coronary heart disease (CHD) 58 .The indirect methyltransferase inhibitor adenosine dialdehyde decreases Atg7 expression and autophagy in cancer cells, indicating that Atg7-related methylation might be a potential target for treating breast and lung cancer 59 .
Another study aimed at finding epigenetic alternations in miRNAs and DNA through an in silico approach identified Atg7 as a hub gene and a potential target for gestational diabetes mellitus (GDM) diagnosis and treatment 60 .
Regulation on Atg7 mRNA Modification and regulation of Atg7 mRNA have been widely discussed in recent decades, including methylation and regulation by miRNA, lncRNA, circRNA, and RNA-binding proteins.The impact of these influential factors on Atg7 can further affect multiple physiological processes and aging-related diseases (Table 2).M 6 A-methylation.N6-methyladenosine (M 6 A) methylation is a common internal modification in eukaryotic mRNA 61 .M 6 A influences almost every fundamental aspect of mRNA metabolism and is controlled by RNA-binding proteins (RBPs), methyltransferase complexes, and demethylases.M 6 A targeting of Atg5 and Atg7 regulates adipogenesis by affecting autophagy.Atg5 and Atg7 are two potential targets of the fatassociated RNA demethylase, FTO 62 .Methyltransferase-like 3 (METTL3)-mediated M 6 A can attenuate Atg7 mRNA stability, decreasing its expression and facilitating cellular aging and osteoarthritis by regulating the autophagy-GATA4 axis.Specifically, METTL3-mediated M 6 A initiates the decay of the Atg7 transcript in a YTH M 6 A RNAbinding protein 2-dependent way 63 .Silencing METTL3 enhances Atg7 mRNA stability and increases its expression.Synovium-targeted METTL3 siRNA downregulates senescence-associated secretory phenotype expression and increases autophagy in osteoarthritis-fibroblastlike synoviocytes, further alleviating cellular senescence in joints and destabilization of the medial meniscus-induced cartilage destruction 63 .METTL3 can regulate Atg7 to reverse drug resistance in chronic myelocytic leukemia cells and gefitinib resistance in NSCLC cells caused by βelemene 64,65 .In addition, Atg7 M 6 A is increased in GDM with obesity 66 .
miRNAs.miRNAs belong to a highly conserved family that controls its downstream gene translation processes 67 .Several miRNAs have Inhibitory effects on Atg7 in heart disease.Heart failure is a chronic disease associated with cardiomyocyte apoptosis and autophagy.MiR-129-5p inhibits autophagy and cardiomyocyte apoptosis, retarding heart failure progression 68 .MiR-143 expression relieves myocardial ischemia/reperfusion (I/R) injury by downregulating Atg7 expression 69 .miR-182-5p and miR-20b-5p play a similar role 70,71 .Indeed, MiR-27a-5p could inhibit Atg7 and had a cardioprotective effect against hypoxia-induced H9c2 cell injury, suggesting it is a potential strategy for healing hypoxia-related heart disease 72 .MiR-542-5p might also be a target for treating heart disease caused by hypoxia/reoxygenation-induced cardiomyocyte injury due to its relationship with Atg7 mRNA 73 .Adipose-derived stromal cellderived exosomes enhanced by miR-93-5p have cardioprotective effects after AMI in an Atg7-targeting pathway that inhibits autophagy and inflammatory response 74 .Similarly, miR-188-3p regulates autophagy and myocardial infarction by altering Atg7 expression 75 .Moreover, atherosclerosis (AS) is also under the control of miR-188-3p by targeting Atg7 76 .MiR-221 negatively regulates FOXO3, inhibits Atg7 transcription, and is a potential target for cardiac fibrosis after myocardial infarction (MI) 77 .The loss of cardiomyocytes after an injury, such as MI, might be compensated by cardiac progenitor cells; miR-143 participates in this process via targeting Atg7 78 .Studies in the Se-deficient chicken model showed that Se deficiency upregulates Atg7 expression and inhibits cardiomyocyte autophagy by modulating miR-17-5p expression 79 .
Emerging studies have shown that miRNAs can directly inhibit Atg7 in some key pathways involved in drug resistance in cancer.MiR-7-5p increases chemoresistance to cisplatin (DDP) in bladder cancer by suppressing invasion and inhibiting Atg7 expression 80 .TRIM65 knockdown in A549/DDP cells downregulates autophagy and DDP resistance via the miR-138-5p/Atg7 axis 81 .Similarly, miR-4486 inhibits autophagy and decreases DDP resistance in HCT116/DDP and SW480/DDP cells by targeting Atg7 82 .MiR-1236-3p also regulates autophagy and DDP resistance via its effects on Atg7 mRNA expression 83 .MiR137 attenuates starvation-induced autophagy and promotes adriamycin sensitivity in U87 cells by regulating Atg7 expression 84 .MiR-615-3p and miR-17 may regulate Atg7 expression and further chemoresistance in NSCLC 85,86 .In addition, the miR-3657/Atg7 axis increases the sensitivity of gastric cancer cells to apatinib 87 .
CircRNAs.CircRNAs are novel RNA molecules characterized by covalently closed loops widely present in eukaryotes 143 .In EOC, circ-EEF2 promotes autophagy by interacting with miR-6881-3p and upregulating its target Atg7 111 .CircRNA RACGAP1 is a sponge for miR-3657 to upregulate Atg7 expression, and circRACGAP1 knockdown increases the sensitivity of gastric cancer cells to apatinib 87 .CircRNA0006948 modulates Atg7 expression levels through the CircRNA0006948/miR-490-3p/ Atg7 pathway, which regulates the invasion, proliferation, and migration of osteosarcoma 144 .CircRNA0092276 regulates the miR-348/Atg7 axis to promote autophagy and the doxorubicin resistance in breast cancer 110 .Autophagy-associated circAtg7 is located in both the nucleus and cytoplasm.Nuclear circAtg7 is a scaffold that strengthens the interaction between Atg7 mRNA and human antigen R protein to stabilize Atg7 mRNA.Cytoplasmic circAtg7 is a sponge for miR-766-5p that increases Atg7 expression.Furthermore, circAtg7 regulates PC cell proliferation and metastasis by modulating autophagy 113 .
Others.RBPs interact with RNA directly via specific RNA-binding domains and participate in many post-transcriptional regulatory processes.The RBP HuR binds to the coding region of Atg7 mRNA to regulate hypoxia-induced autophagy 146 .Additional mechanistic studies showed that HuR increases Atg7 mRNA stability by binding to its AUrich elements 147 .This interaction mainly occurs in patients with diabetic intervertebral disc degeneration or under hypoxia conditions 146,147 .RBP LIN28A also interacts with Atg7 mRNA, which might be the target for LIN28A regulation at the post-transcriptional level.This interaction can increase Atg7 mRNA stability and protein levels and promote chemoresistance in breast cancer 148 .
U2AF35 belongs to the splicing factor SR gene family, which is frequently mutated in various diseases.Recurrent mutations in U2AF35 (S34F) have been observed in myelodysplastic syndrome and tumors and promote transformation by generating aberrant Atg7 pre-mRNA 3' ends.In U2AF35(S34F)-transformed cells, the Atg7 pre-mRNA is processed incorrectly, leading to secondary mutations 149 .
Post-translational modifications of the ATG7 protein ATG7 can be modulated during autophagy by several post-translational modifications, including acetylation, deacetylation, and ubiquitination.
Acetylation and deacetylation.The p300 acetyltransferase regulates the acetylation of various autophagy proteins.Disruption of p300 can reduce ATG7 acetylation and stimulate autophagy, while p300 overexpression increases ATG7 acetylation and inhibits starvation-induced autophagy 150 .BCL2-associated athanogene 6 (BAG6)/HLA-B-associated transcript 3 increases p53 acetylation and limits the p300dependent acetylation of ATG7 151 .Additionally, BAG6 tightly controls p300 intracellular localization, influencing the accessibility of p300 to ATG7 and p53 and controlling autophagy 151,152 .Under various pathophysiological conditions, the beta chain of the non-classical MHC-II protein HLA-DM restricts the human T-cell leukemia virus type-1 (HTLV-1) expression by directly interacting with ATG7 and regulating ATG7 acetylation promoted by p300 153 .A histone acetyltransferase encoded by the M. oryzae ortholog of GCN5 acetylates ATG7, downregulating light-and nitrogen-starvation-induced autophagy in response to important environmental changes 131 .
The NAD-dependent deacetylase Sirt1 regulates autophagy and the cellular starvation response 154 .Sirt1 mediates chondrocyte autophagy by physically interacting with and deacetylating ATG7 155 .Osteoarthritis (OA) is an age-related degenerative disorder accompanied by pain and joint mobility disturbances.Sirt1 levels decrease in aged or OA cartilage compared to young and healthy cartilage.Sirt1 deacetylates the lysine residues on ATG7 and other crucial autophagy proteins to increase autophagy in chondrocytes.Chondrocyte-specific Sirt1 silencing decreases chondrogenic markers.Thus, Sirt1 is a potential target for OA intervention 156 .Aldehyde dehydrogenase 2 (ALDH2)-enhanced Sirt1 modulates the interaction between LC3 and ATG7.ALDH2 activation in aging hearts enhances LC3 deacetylation in the nucleus and the formation of LC3-ATG7 complexes in the cytoplasm by controlling Sirt1 activation and nuclear localization 157 .
Ubiquitination.The ubiquitination of proteins plays a role in proteasome degradation, immune response regulation, mitochondrial autophagy, epigenetic regulation, and apoptosis 159 .Recent studies have indicated that the RING-type E3 ligase, tripartite motif-containing protein (TRIM) 7/RNF90, promotes ATG7 ubiquitination.TRIM7 is a core factor in infection-, starvation-and rapamycin-induced autophagosome accumulation.It helps host cells resist bacterial infection by inducing the K63-linked ubiquitination of ATG7 at K413 to positively regulate autophagy.Moreover, experiments in mouse models have shown that ATG7 ubiquitination at K413 or K409 has a decisive impact on L. monocytogenes infection and host cell resistance.Autophagosome accumulation after L. monocytogenes infection of wild-type cells but not cells with TRIM7 or ATG7 inactivating mutations clears intracellular bacteria and exerts defensive effects 160 .
Oxidative stress-induced autophagy helps prevent cell damage and maintains cellular homeostasis 161 .Previous studies have shown that ROS activates the ataxia-telangiectasia mutated (ATM)-cell cycle checkpoint kinase 2 (CHK2) pathway and promotes autophagy.When the ATM/ CHK2 pathway is activated by ROS, ATM and CHK2 phosphorylation leads to TRIM32 phosphorylation at S55, activating its E3 ubiquitin ligase function.TRIM32 activation causes ATG7 K63-linked ubiquitination at K45, initiating ROS-induced autophagy.In addition, Liu et al. showed that

Review article
the ATM/CHK2/TRIM32/ATG7 axis might alleviate I/R injury in mice by activating autophagy 162 .

ATG7 functions and its relationship with aging-related diseases
ATG7 plays a crucial role in two ubiquitin-like conjugation systems involving ATG12 and LC3 163 .The ubiquitin-like conjugation system involving ATG12 also contains ATG7, ATG5, ATG16, and ATG10; the ATG12-ATG5-ATG16 complex forms an E3 ligase 6,7 .ATG7 catalyzes another ubiquitin-like conjugation system with ATG3 and ATG4 for the lipidation of LC3 164 .On this basis, the classical autophagy function and related regulatory mechanism of ATG7 are involved in several physiological processes and aging diseases.Several studies have indicated that ATG7 has additional functions beyond autophagy.

Autophagy-dependent functions of ATG7
Cell fate.Theoretically, autophagy and apoptosis are crucial catabolic processes regulating cell maintenance and tissue homeostasis 165 .ATG7 promotes apoptosis, prevents epithelia-mesenchymal transition (EMT), and inhibits proliferation by blocking aerobic glycolysis in the mitochondria of triple-negative breast cancer (TNBC) cells 166 .Studies with human periodontal ligament cells also demonstrated that ATG7 overexpression contributes to the proliferation and inhibits apoptosis in aging cells 167 .Autophagy is renoprotective during AKI, especially in vancomycin (Van)-induced AKI 168 .Researchers found that the cell deathrelated gene, PKC-δ, was markedly suppressed in the Atg7-KO model after Van treatment.ATG7 might induce renal cell apoptosis after Van treatment by binding to PKC-δ 168 .
TNFAIP8 interacts with the ATG7-ATG3 complex and facilitates LC3 lipidation.The TNFAIP8-ATG7 interaction is important in regulating autophagy and proliferation in liver cancer cells 169 .Alzheimer's disease (AD) is a common neurodegenerative disorder mainly caused by β-amyloid (Aβ) peptide accumulation.Estrogen receptor β can promote autophagy by interacting with ATG7, which further improves the autophagy-lysosomal activity in Aβ clearance and decreases the risk of AD 170 .
ATG7 regulates the cell cycle and thrombopoiesis during hematopoiesis, counteracting hematopoietic aging and leukemogenesis at multiple stages.ATG7-dependent canonical autophagy is critical for hematopoietic stem cells, but not for differentiated or somatic cells 171 .Atg7-KO mice are more prone to engrafted leukemogenesis, demonstrated by increased white blood cells, lymphocytes, and platelets.ATG7 deletion causes the deterioration of hematopoietic stem and progenitor cell (HSPC) function, which may lead to leukemogenesis 172 .Additional mouse studies revealed that the loss of ATG7 in HSPCs led to a lethal pre-leukemic phenotype 173 .Autophagy is implicated in the cell cycle of HSPCs in a nutrient-dependent manner; the absence of ATG7 leads to the ablation of the HSCPs cell cycle 174 .Transcriptomic analysis of HSPCs suggested that hematopoietic ATG7related autophagy defects caused elevation of iron activity, inhibited osteocyte differentiation and calcium metabolism, potentially leading to bone loss and osteoporosis 175 .Atg7-deficient models had mitochondrial and cell cycle dysfunction, impaired platelet production, and failed hemostasis 176 .In addition, abolishing ATG7-related autophagy in the hematopoietic system greatly impacts the aging of non-hematopoietic organs 177 .
Reduced osteoblast differentiation is critical in bone-related pathogenesis, including OA and osteoporosis.Ferutinin significantly increases the expression of KLF2, ATG7, and several other autophagy-related proteins in dental pulp-derived stem cells.In contrast, Atg7-or Beclin1-KO reduces KLF2 and the levels of osteoblast (OB) differentiation-related molecules, indicating that ferutinin regulates OB differentiation via KLF2 and autophagy 178 .ATG7 and superoxide dismutase 2 are involved in the pathogenesis of osteoporosis, and their expression levels correlated in osteoporotic mice and osteoporosis-free mice 179 .Another study using dexamethasone-induced osteoporotic mouse models suggested that glucocorticoid-induced bone loss enhanced ATG7-related autophagy in osteoclasts via the PI3K/Akt/mTOR signaling pathway 180 .
Cell structure and development.The lamellar body (LB) is a specific lysosome-related organelle in type 2 alveolar epithelial cells, specifically related to autophagy 181,182 .Atg7-KO in mice interrupts the maturation process of LB and the production of surfactant protein B, indicating that ATG7 is necessary for the formation, maturation, and maintenance of LB 183 .In addition, suppression of AMP-activated protein kinasemediated autophagy leads to poor lung development or even bronchopulmonary dysplasia 184 .
Increased ATG7 in neural tubes promotes neural crest cell delamination by suppressing the BMP4/Smad signaling pathway.Moreover, ATG7 overexpression accelerates cell progression toward S phase 185 .Additionally, research using ATG7 heterozygous mice suggested that ATG7 is involved in progeria by modulating autophagy 186 .
ATG7 regulates cerebrovascular development by promoting endothelial fibronectin expression and modulating Protein kinase A activity.Atg7-endothelial knockout (eKO) reduces fibronectin expression and causes cerebral astrocyte-microvascular disassociation, impairing the bloodbrain barrier homeostasis 187 .ATG7 deletion leads to frustration in epinephrine-stimulated von Willebrand factor (VWF) secretion accompanied by prolonged bleeding time.Moreover, the processing, maturation, and secretion of VWF in endothelial cells is controlled by ATG7-mediated autophagy 188 .In chick embryos, ATG7 expression is observed in the plexus vessels of angiogenesis, and interruption of autophagy blocks angiogenesis by altering cell viability and migration 189 .Ethanol exposure can enhance autophagy by upregulating LC3 and ATG7 expression levels.After ethanol treatment, the incidence rate of congenital cardiovascular diseases in chick embryos increases 190 High-glucose levels increase ATG7 and LC3 expression, indicating that autophagy may also be involved in high-glucoseinduced cardiovascular malformation 191 .
ATG7 prevents EMT by suppressing aerobic glycolysis 166 .During EMT, epithelial cells lose their cell polarity, resulting in higher mesenchymal phenotypes that might affect the progression of malignant tumors derived from epithelial cells 192 .Altered ATG7 expression levels correlate with tumor progression and prognostic outcomes in TNBC 166 .In Atg7-KO retinal pigment epithelium (RPE) cells, the epithelial marker claudin-1 is reduced, while mesenchymal markers are decreased, leading to cell migration and enhanced contractility.ATG7-mediated autophagy is a notable mechanism in EMT resistance 193 .Research with chicken embryos has shown that ATG7 affects whole embryonic development by regulating EMT.During EMT in gastrulation, ATG7 expression is observed on the top of the endoderm and ectoderm.E-cadherin, a marker of EMT, increases when ATG7 is overexpressed 194 .
Others.It has been reported that ATG7(−/−) mitochondria have deficiencies in mitochondrial respiration.Reduced resting mitochondrial oxygen consumption, increased compensatory basal glycolytic rates, and increased steady-state ROS levels have been observed in ATG7(−/−) cells.Pancreatic beta cell-specific Atg7-KO mice exhibit mitochondrial dysfunction along with oxidative stress, indicating the important role of ATG7 in glucose metabolism 195 .Impaired ATG7-mediated autophagy enhances muscle loss and sarcopenia in the aging population, and betaine can regulate autophagy to stop degeneration in aged muscle 196 .Moreover, a proteotoxic heart failure study suggested that ATG7-induced autophagy could decrease cardiac hypertrophy and interstitial fibrosis, ameliorate ventricular dysfunction, and reduce intracellular aggregates 197 .In addition, the regulation of nuclear factor-kappaB (NF-κB) by ATG7 can also affect drug resistance in cancer cells.The blockade of ATG7mediated autophagy interrupts IκB degradation by inhibiting cathepsin D, which further activates the NF-κB signaling pathway, which can influence the drug sensitivity of cancer cells 198 .
Autophagy-independent functions of ATG7 Cell fate.The transcription factor p53 is a key tumor suppressor that plays fundamental roles in cancer immunity and inflammation 199 .It is also involved in many cellular functions, including metabolism, DNA https://doi.org/10.1038/s42003-024-06080-1repair, cell cycle arrest, cell differentiation, senescence, and cell death 200 .Previous studies have shown a significant relationship between p53 and autophagy-related proteins, especially ATG7 201,202 .The absence of ATG7 can increase mitochondrial ROS and DNA damage, affect cell cycle inhibitor p21 expression, and reciprocally regulate p53-dependent cell cycle and cell death pathways by activating p53.These observations demonstrated reciprocal regulation in which ATG7 can bind to and regulate p53 and further modulate the cell cycle and survival during metabolic stress 203 .Cnot-3, a component of the CCR4-NOT complex, can shorten the poly(A) tail of Atg7 mRNA.ATG7 and p53 coimmunoprecipitate from Cnot3-KO heart lysates, showing that these two proteins interact.Additional research indicated that the nuclear ATG7 and p53 levels increased in Cnot3-KO cells compared to wild-type cells, and nuclear ATG7 modulated p53 activity to induce the expression of cell death-promoting factors 204 .A recent study showed that ATG7, p53, and VIM3 form a complex in prostate cancer and BPH-1 cells.Moreover, the VIM3/p53/ATG7 complex affected the migration of prostate cancer cells by binding with the pri-miR-371a-3p promoter, providing a novel method of prostate carcinoma differentiation 205 .
Metabolic reprogramming.The Warburg effect is a special energy metabolic process first described in cancer cells.This effect is frequently found in cancer tissues and many other rapidly dividing normal cells 206 .Autophagy provides a mechanism by which cells can cope with energy crises and is associated with energy metabolism in tumor cells.ATG7 inhibits the Warburg effect by binding PKM2 and preventing its phosphorylation on Tyr-105 by FGFR1 207 .Loss of ATG7 produces the opposite result, promoting EMT in tumor cells.The link between ATG7 and the Warburg effect could provide new strategies for cancer treatment 207 .
NF-κB.Research has shown that ATG7 exerts its effects by regulating transcription.The proangiogenic activity of ATG7 in the brain is mediated by IL-6 production, which is dependent on NF-κB 208 .Atg7-eKO can alleviate brain inflammatory responses after I/R in mice.Atg7-eKO reduces IKKβ phosphorylation, which inactivates NF-κB and decreases the mRNA levels of several pro-inflammatory cytokines, including IL-6 and IL-8.Interestingly, transcriptional regulation by ATG7 is independent of its role in autophagy 209 .
Inflammation and ATG7 have a complicated relationship in bone disease.Inflammation inhibits autophagy, proliferation, and the cell cycle in chondrocytes, manifested by arrest in G1, a reduced S phase, and downregulation of ATG7, ATG5, p62, and LC3.Inhibiting the PI3K/AKT/mTOR signaling pathway relieves inflammatory responses in OA rat models 210 .Increased Grb2-associated-binding protein-2 (GAB2) in chondrocytes correlates with OA progression in in vivo and in vitro OA models.Furthermore, GAB2 inhibition decreases p62 expression but increases the expression of ATG7 and other autophagy-related proteins 211 .
Others.ATG7 is also essential for counteracting hematopoietic aging.Knocking out Atg7 or Atg5 showed that ATG7 plays a non-autophagic role in maintaining normal nucleosome assembly and decelerating aging in the CD11b(+)Ly6G(−) cell population in the bone marrow.ATG7 deletion significantly confers an aging phenotype on this blood lineage subgroup.These results indicate a dual role for ATG7 in resisting hematopoietic aging 212 .In addition, ATG7 promotes OCT4 transcription and stem-like properties by interacting with and stabilizing β-catenin.This mechanism may promote the cancer stem-like cell characteristics of prostate cancer, including tumor initiation, self-renewal, and drug resistance 213 .

Summary and future directions
ATG7, an E1-like ubiquitin-activating enzyme, promotes the formation and extension of autophagosome membranes, thus initiating cellular autophagy.The basic autophagy-dependent functions of ATG7 involve two ubiquitin-like conjugation systems-ATG12-ATG5 and LC3phosphatidylethanolamine.Besides its E1-like effects in autophagy, whether ATG7 could serve as an E1 enzyme in ubiquitination reactions needs to be clarified.
ATG7 protein is involved in many aging diseases and could serve as a promising therapeutic target (Fig. 4).Importantly, ATG7 plays different roles in various tissues.Muscle-specific deletion of ATG7 downregulates muscle mass and strength and causes abnormal mitochondria and swollen sarcoplasmic reticulum.Excessive activation of ATG7-mediated autophagy also induces severe muscle loss 214 .VSMC-specific Atg7-KO causes sarcoplasmic reticulum swelling and imbalanced Ca 2+ homeostasis, leading to altered contractility 215 .In colon epithelial conditional Atg7-KO mice, experimental colitis deteriorated, with more bacterial intrusion into the colonic epithelium.Furthermore, the expression of antimicrobial or antiparasitic peptides and the secretion of colonic mucins were diminished in the conditional Atg7KO mice, leading to abnormal microflora and colitis 216 .Mice deficient for pancreatic ATG7 suffered earlier death caused by inflammation, fibrosis, increased apoptosis and necroptosis, and declining exocrine and endocrine functions 217 .Experiments in the drosophila eye revealed that both ATG7 and Hsp27 are involved in normal eye development.Overexpression of ATG7 could rescue Hsp27-deficient phenotypes; however, overexpression of Hsp27 could not rescue ATG7-deficient phenotypes 218 .ATG7 also participates in liver pathology and the adiposeliver system.Adipocyte-specific loss of Atg7 enhances high-fat diet (HFD)induced inguinal white adipose tissue hypertrophy, which downregulates serum-free fatty acid levels and relieves HFD-induced steatosis, liver inflammation, and fibrosis through adipose-liver crosstalk 219 .In certain diseases (e.g., AKI), activating ATG7-mediated autophagy might alleviate the symptoms.Understanding the various roles of ATG7 in different tissues Multiple genetic and transcriptional mechanisms regulate the autophagy-dependent functions of ATG7.Transcription factors, transcriptional regulatory factors as well as miRNA, circRNA, lncRNA, and RBPs regulate Atg7 mRNA expression.Moreover, various post-translational modifications regulate ATG7 protein function.Although multiple regulatory mechanisms have been defined for the autophagy-dependent functions of ATG7, how the autophagy-independent functions of ATG7 are regulated remains unclear.Because ATG7 might be regulated differently when performing autophagy-dependent and autophagy-independent functions, it is important to determine how ATG7 switches between its autophagy-dependent and autophagy-independent roles.
DNA methylation can control genetic expression without altering DNA sequence by changing chromatin structure, DNA conformation, DNA stability, and DNA-protein interactions.Until recently, little was known about the DNA methylation of Atg7 and its functions.One study reported that Atg7 gene methylation can be affected by Legionella Infection, which causes a reduction in Atg7 mRNA 57 .The studies in monocytes and peripheral blood leukocytes showed that the methylation status and expression status of Atg7 might clue a novel epigenetic mechanism for CHD 58 .The epigenetic modifications of Atg7, including DNA methylation, require further study.Methylation is an important post-translational modification that adds methyl groups to amino acid residues in proteins, thereby altering protein structure and function.Methylation of a protein can regulate its stability, localization, and interactions, significantly affecting biological processes, including gene expression and cellular signaling.The methylation and other possible post-translational modifications of ATG7 protein are likely to have significant implications, and further research in this field is needed.
Along with the improvement of technologies and a comprehensive understanding of ATG7 regulatory mechanisms, it is anticipated that targeting ATG7 could benefit aging-related diseases.Future research should elucidate the specific molecular mechanisms underlying how ATG7 exerts its multiple functions and how these functions are related to aging diseases and corresponding therapies.
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Fig. 2 |
Fig. 2 | Classical autophagy process mediated by ATG7 as E1-like enzyme.ATG7 protein is a homodimeric E1 enzyme that mediates covalent modifications of other autophagy-related proteins during autophagy, including the binding of ATG5 and ATG12, and the lipidation of LC3.

Fig. 4 |
Fig. 4 | An overview of ATG7 function and regulatory mechanism.ATG7 is regulated at DNA, mRNA, and protein levels, and is closely associated with transcription regulation, cell fate, energy metabolism, developmental regulation and aging diseases.

Table 1 |
Representative Atg7-KO animal models Whole body Lower mean body weight and earlier death, partly caused by the interrupt of amino acids recycling Disrupted cell cycle Enhanced HFD-mediated NRF2 downregulation, possibly influencing the degree of liver damage and the development of hepatic steatosis Enhanced macrophage activation and Concanavalin A-induced acute hepatitis Viscus Kidney In inducible, renal tubule-specific Atg7-KO mice, the pro-fibrotic phenotype of tubular cells is induced.Meanwhile, fibrosis is down-regulated after AKI.